How evolutionary forces interact to maintain genetic variation within populations has been a matter of extensive theoretical debates. While mutation and exogenous gene flow increase genetic variation, stabilizing selection and genetic drift are expected to deplete it. To date, levels of genetic variation observed in natural populations are hard to predict without accounting for other processes, such as balancing selection in heterogeneous environments. We aimed to empirically test three hypotheses: (i) admixed populations have higher quantitative genetic variation due to introgression from other gene pools, (ii) quantitative genetic variation is lower in populations from harsher environments (i.e., experiencing stronger selection), and (iii) quantitative genetic variation is higher in populations from heterogeneous environments. Using growth, phenological and functional trait data from three clonal common gardens and 33 populations (522 clones) of maritime pine (Pinus pinaster Aiton), we estimated the association between the population-specific total genetic variances (i.e., among-clone variances) for these traits and ten population-specific indices related to admixture levels (estimated based on 5165 SNPs), environmental temporal and spatial heterogeneity and climate harshness. Populations experiencing colder winters showed consistently lower genetic variation for early height growth (a fitness-related trait in forest trees) in the three common gardens. Within-population quantitative genetic variation was not associated with environmental heterogeneity or population admixture for any trait. Our results provide empirical support for the potential role of natural selection in reducing genetic variation for early height growth within populations, which indirectly gives insight into the adaptive potential of populations to changing environments.

进化力量如何相互作用以维持种群内的遗传变异一直是广泛的理论争论的问题。虽然突变和外源基因流增加了遗传变异，但稳定选择和遗传漂变预计会耗尽遗传变异。迄今为止，在不考虑其他过程（例如异质环境中的平衡选择）的情况下，很难预测在自然群体中观察到的遗传变异水平。我们的目的是通过实证检验三个假设：（i）由于其他基因库的渗入，混合群体具有较高的数量遗传变异，（ii）来自更恶劣环境（即经历更强的选择）的群体的数量遗传变异较低，以及（iii） ）来自异质环境的种群的数量遗传变异较高。利用增长，松树Aiton），我们估计了这些性状的群体特异性总遗传方差（即克隆间方差）与与混合水平（基于 5165 个 SNP 估计）、环境时空异质性和相关的 10 个群体特异性指数之间的关联。气候恶劣。在三个常见花园中，经历寒冷冬季的种群在早期身高生长（林木中与健康相关的特征）方面始终表现出较低的遗传变异。群体内数量遗传变异与任何性状的环境异质性或群体混合无关。我们的结果为自然选择在减少种群内早期身高增长的遗传变异方面的潜在作用提供了实证支持，